Accident Overview
A midair collision occurred between a Cessna and a Piper over a remote area at an altitude of approximately 1,760 ft mean sea level. The Cessna had departed about three minutes prior on a scheduled passenger flight, while the Piper was en route to a remote hunting camp. The weather was day visual meteorological conditions. Both pilots and all passengers sustained fatal injuries, and both airplanes were destroyed.
Investigation Findings
Postaccident examination revealed signatures consistent with the Cessna's outboard left wing initially impacting the Piper's right wing forward strut while both aircraft were in level cruise flight. No mechanical malfunctions or anomalies were found that would have precluded normal operation of either airplane. Neither pilot was in communication with an air traffic control facility, nor were they required to be.
Performance and Visibility Study
A performance and visibility study indicated that each airplane would have appeared as a relatively small, slow-moving object in the other pilot's field of view, with fuselages spanning less than 0.5° of the field of view—equivalent to the diameter of a penny viewed from about 7 ft away. This condition persisted until approximately 10 seconds before the collision, at which time the aircraft would have appeared to grow in size suddenly, known as the "blossom" effect. From about two minutes before the collision, neither airplane would have been obscured from the other pilot's nominal field of view by cockpit structure, though the Cessna would have appeared close to the bottom of the Piper's right wing and near the forward edge of its forward wing strut.
Cockpit Technology and See-and-Avoid
The Cessna was equipped with Automatic Dependent Surveillance-Broadcast (ADS-B) Out, but the Piper was not ADS-B equipped. Neither airplane had a cockpit display of traffic information (CDTI). The study determined that CDTI would have presented visual information regarding the potential conflict to both pilots beginning about 2 minutes 39 seconds before the collision, and auditory information beginning about 39 seconds before the collision, providing adequate time for the pilots to react.
The see-and-avoid concept requires pilots to look through cockpit windows, identify other aircraft, decide if any are collision threats, and take appropriate action. The investigation noted inherent limitations of this concept, including limitations of human visual and information processing systems, competing pilot tasks, limited field of view from the cockpit, and environmental factors that can diminish aircraft visibility. Given the remote operating area, it is likely that the pilots had relaxed their vigilance in looking for traffic.
Probable Cause
The probable cause (official findings) is the failure of both pilots to see and avoid each other while in level cruise flight, which resulted in a midair collision.
Autopsy of the Cessna pilot was inconclusive for natural disease due to trauma; it was undetermined if natural disease could have presented a significant hazard to flight safety.